Which rank is one level above Commander (CDR)?

The rank that is one level above Commander (CDR) is Captain (CAPT). In the naval rank structure, the progression goes from Lieutenant Commander (LCDR) to Commander (CDR), and then to Captain (CAPT). Understanding this hierarchy is crucial for recognizing the leadership and command structure within the Coast Guard and other military branches.

Lieutenant Commander (LCDR) is a rank below Commander, making it not a viable option for this question. Rear Admiral Lower Half (RDML) is the next rank above Captain, thus it exceeds the single level above CDR being asked. Chief Warrant Officer 4 (CWO4) operates in a different rank category entirely, and when comparing it to the line officer ranks, it does not fit into the direct progression from Commander. Thus, Captain (CAPT) is indeed the correct and relevant answer in the context of this question.